1. Piston Removal

★ Following the internal combustion engine disassembly sequence, first remove components such as the cylinder head, intake manifold, and exhaust manifold, exposing the upper surface of the cylinder liner.
★ Use a torque wrench to loosen the connecting rod bolts in the prescribed sequence (typically starting from the center and working outward in stages), then remove the rod caps along with the connecting rod bearings. Be sure to mark the connecting rods and rod caps for proper reassembly (e.g., use a marker to indicate the cylinder number).
★ Gently tap the top of the piston using a specialized tool or a soft wooden rod to remove the piston along with the connecting rod from the upper end of the cylinder liner—taking care to avoid scraping the piston skirt against the inner wall of the cylinder liner.

2. Piston Component Inspection

Piston Body Inspection

★ Visual Inspection: Examine the piston top for carbon deposits, cracks, or burn marks. If carbon buildup is thick, carefully document its distribution. Also, check the piston skirt for scratches, wear marks, and ensure the surface coating remains intact—looking for any signs of peeling or flaking.
★ Dimension Measurement: Use a micrometer to measure the piston skirt diameter (typically at positions 1/3 and 2/3 of the skirt height from the piston top, measured perpendicular to the axis of the piston pin bore). Compare these measurements with the original factory specifications. If wear exceeds 0.15 mm or cylindricity error surpasses 0.05 mm, the piston must be replaced.
★ Piston Pin Bore Inspection: Use a dial indicator to measure the inner diameter of the piston pin bore, checking for wear or ovality errors on the bore walls. If the clearance between the bore and the piston pin exceeds the manufacturer’s specified tolerance (typically 0.005–0.015 mm), the piston should be repaired or replaced.

Piston Ring Inspection

★ Visual Inspection: Check the piston rings (gas ring and oil ring) for cracks, deformation, wear, or corrosion marks. Also, inspect the outer circular surface of the gas ring for scratches, and ensure the oil ring scraper blades retain sufficient elasticity.
★ Gap Measurement: Insert the piston ring into a standard cylinder liner (or a dedicated inspection sleeve) and use a feeler gauge to measure the piston ring end gap (the end gap for gas rings typically ranges from 0.25 to 0.5 mm, while for oil rings it’s usually 0.3 to 0.6 mm). If the gap is too large or too small, the piston ring must be replaced. Next, measure the piston ring side clearance (the radial clearance between the ring and its groove): gas rings generally have a side clearance of 0.03 to 0.07 mm, while oil rings require a clearance of 0.02 to 0.05 mm. If the clearance falls outside these ranges, replacement is necessary.
★ Connecting Rod and Piston Pin Inspection: Check the connecting rods for bending, twisting, or deformation. Use a connecting rod straightness gauge to measure any straightness errors—if the error exceeds 0.05 mm/100 mm, the rod must be straightened. Also, inspect the piston pin surface for wear or scratches, ensuring that the clearance between the pin and the small-end bushing of the connecting rod meets the manufacturer’s specifications.

3. Component Cleaning

★ Dip a cleaning brush into the specialized metal cleaner, and carefully remove carbon deposits from the top of the piston and within the ring grooves—taking care to avoid scratching the piston surface. For stubborn carbon buildup, first use compressed air to blow away loose debris, then soak the area in the cleaner for 10–15 minutes before scrubbing with the brush.
★ Clean oil stains and carbon deposits from the surface of the piston rings, use compressed air to clear the oil return holes in the oil rings, ensuring they remain unobstructed; also clean components such as connecting rods, piston pins, and retaining rings, removing any surface impurities. After washing, dry thoroughly with a clean cloth and apply a small amount of lubricant to prevent rust.
★ Use compressed air to blow away any remaining impurities and carbon deposits from the cylinder liner inner wall, then inspect the liner for signs of wear. If severe scoring is found, the cylinder liner must be repaired first.

4. Piston Assembly

★ Before assembly, apply a thin layer of lubricant to the piston pin bore and the surface of the piston pin. Carefully insert the piston pin into the bore, then install the retaining rings at both ends, ensuring they are fully seated in their grooves without any looseness.
★ Use the piston ring compressor pliers to install the oil ring and gas rings one by one (pay attention to the correct installation sequence of the gas rings—typically, the first gas ring is a chrome-plated ring, while the second is a standard gas ring—with the openings staggered. Ensure that adjacent ring openings are spaced at least 90° apart and avoid aligning them directly with the piston pin bore axis). When installing, take care to prevent the piston rings from bending or breaking.
★ Apply a suitable amount of lubricant to the piston skirt and piston ring surfaces, then carefully insert the piston—along with the connecting rod—into the cylinder liner (make sure the mark on the piston top aligns with the corresponding cylinder to prevent incorrect installation). Use a specialized tool to gently press down on the piston rings, ensuring the piston slides smoothly into the cylinder without scratching the cylinder walls.
★ Install the connecting rod cap and connecting rod bearings (ensure alignment of matching marks), then tighten the connecting rod bolts in stages using a torque wrench to the specified torque (refer to the manufacturer’s technical manual—typically 25–40 N·m)—following an alternating sequence from the center outward toward both ends.